Method of measuring properties of an object with acoustically induced electromagnetic waves

ABSTRACT

A measuring method and apparatus in which a measurable object ( 23 ) is irradiated with acoustic waves to measure a change in property value of charged particles in the object from electromagnetic waves induced thereby. A part ( 2 ) of the measurable object irradiated with an acoustic focused beam ( 1 ) is in a charge distribution state in which positive charged particles ( 3 ) are greater in number in the part ( 2 ) where electromagnetic waves induced by positive charged particles ( 3 ) are not canceled by those induced by negative charged particles ( 4 ) and where net electromagnetic waves ( 6 ) are induced. Since a change in concentration of positive charged particles ( 3 ) and/or negative charged particles ( 4 ) changes the intensity of electromagnetic waves ( 6 ), it is possible to know such a change in concentration of the charged particles from a change in intensity of electromagnetic waves ( 6 ).

TECHNICAL FIELD

The present invention relates to a method of and an apparatus formeasuring properties of an object of every sort, including a human body,which when acoustically vibrated may be capable of emittingelectromagnetic waves, from such electromagnetic waves induced byapplicable sound waves. The present invention relates in particular to atechnique using such a method for the measurement of an active site of abrain.

BACKGROUND ART

In the interest of elucidating a relation between a human mentalactivity and a brain's action and in an effort to specify a lesion inbrain's disease therapeutics, attempts have been made to identify aneural active site of the brain. Neurons in a neural activity control anion concentration to form a charge distribution and transmit informationthrough propagation of a potential created by the charge distribution,namely of an action potential (see Non-patent Reference 1). Thus, themost direct information source that can identify a site of neuralactivity is the action potential, more cardinally the chargedistribution which the neuron creates.

While in the measurement of an action potential in the nervous system, amethod is usually taken in which to directly insert an electrode intothe body, use cannot be made of this method for a human body, inter aliafor its brain tissue but necessarily of a noninvasive measuring methodto identify an active region from the outside of the human body withoutharming the body part.

As the noninvasive method of measuring a neural activity, PET (positronemission tomography; see Non-patent Reference 2), fMRI (functionalmagnetic resonance imaging; see Non-patent Reference 3), near infraredtopography (see Non-patent Reference 4) and magneto-encephalography (seeNon-patent Reference 5) have been primarily put to practical utilizationat present.

In any of PET, fMRI and near infrared topography, however, in whichneuron's activity is indirectly detected from a change in amount ofmetabolism, namely in amount of bloodstream in the blood or oxygentherein, in the region of an active site, no electrical signal createdby neurons is directly measured. As a result, their position and timeresolutions for an active site are not sufficient in elucidating arelation between a human mental activity and a brain's action or inserving for disease therapy. They require a cyclotron accelerator forproducing positrons, a high field generating apparatus for nuclearmagnetic resonance or the like and are extremely high in apparatus cost.

Magneto-encephalography which detects a very weak magnetic field asinduced by an intracellular electric current is a process that is highin time resolution as it detects neurons' activity more directly than dothe others above. This method in which a position is estimated on thebasis of a magnetic field distribution and hence determined indirectlyis not enough in position resolution. Especially if a plurality of sitesare active simultaneously, their identification then becomes difficult.There is also the problem that it is difficult to detect informationfrom a deep part and an electric current passed towards a normal to asurface.

Included in properties of a material is a magnetic property. As regardsthe magnetization of a magnetic material, it is reported in Non-patentReference 8, for example, that a ferromagnetic thin film irradiated withlaser light of femtoseconds is observed to produce a coherent radiationin a THz band.

-   Non-patent Reference 1: Michikazu Matsumura “Invitation to Brain    Science (The secret of a neural circuit is expounded)” (in Japanese)    Science Co., Ltd., Jul. 10, 2003, first Ed. third print issue, pp.    55-65;-   Non-patent Reference 2: M. I. Posner & M. E. Raichele (translated    into Japanese by Takeshi Yoro, Masako Kato and Kiyoto Kasai)    “Observing the Brain—The riddle of the mind that the cognitive    neuroscience reveals” (in Japanese) Nikkei Science Co., Ltd., Jun.    25, 2002, third print issue;-   Non-patent Reference 3: P. Jezzard, P. M. Matthews, S. M. Smith    edited “Functional Mri: An Introduction & Methods”, Oxford Univ. Pr    (Sd), ISBN: 01985277 3X, (2003/06);-   Non-patent Reference 4: Michikazu Matsumura “Invitation to Brain    Science (The secret of a neural circuit is expounded)” (in Japanese)    Science Co., Ltd., Jul. 10, 2003, first Ed. third print issue, p.    173;-   Non-patent Reference 5: Michikazu Matsumura “Invitation to Brain    Science (The secret of a neural circuit is expounded)” (in Japanese)    Science Co., Ltd., Jul. 10, 2003, first Ed. third print issue, pp.    168-169;-   Non-patent Reference 6: http://www.rofuku.go.jp/hanasi/eswl. htm;-   Non-patent Reference 7: http://www.edap-hifu.com/; and-   Non-patent Reference 8: E. Beaurepaire and five others, Appl. Phys.    Lett., Vol. 84, No. 18, pp. 3465-3467, May 3, 2004.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Identifying an active site in a brain that is related to a particularmental activity is an extremely effective means for elucidating arelation between a human mental activity and a brain's action, anddetermining in a therapy of a brain's disease if the activity of aparticular site in a brain is normal or abnormal is extremely importantto cure the brain's disease.

As will have been appreciated from the description above, however, theproblem remains that neither the prior-art method of detecting a changein amount of metabolism in the blood to indirectly determine an activesite nor the prior-art method of detecting a very weak magnetic field asinduced by an intracellular electric current with the excitation of aneuron is sufficient in position resolution, and they are incapable ofidentifying an active site with necessity and sufficiency and yet areextremely high in apparatus cost.

In view of the problems mentioned above, it is an object of the presentinvention to provide a method of and an apparatus for measuring a changein property value of charged particles in an object, fromelectromagnetic waves induced by irradiating the object with acousticwaves, namely from acoustically induced electromagnetic waves and, inparticular, a process of determining an active site in a brain to whichthe method is applied and which is capable of detecting a neuron'scharge distribution which is representative of the most direct quantityof a neuron's activity to identify the active site in the brain at ahigh position resolution.

Means for Solving the Problem

As viewed microscopically, an object or substance necessarily comprisesparticles with positive charges and those with negative charges which asa whole are neutral. For instance, Si crystal is made up of a Si corehaving positive charges and electrons revolving around the core andhaving negative charges, which are neutral as a whole. An ionic crystalis made up of cations and anions which as a whole are neutral. Acolloidal solution consists of colloidal particles with positive ornegative charges and ions or molecules surrounding a colloidal particleand with charges opposite in sign to those of the colloidal particlewhich in toto are neutral. Further, a biological liquid in a livingorganism comprises cations such as of Na, K or the like and anions of Clor the like which are neutral as a whole.

The particles which make up a part of an object which is irradiated withacoustic waves are caused to oscillate harmonically at an acousticfrequency and, based on the harmonic oscillations of their charges, thecharged particles generate electromagnetic waves at the acousticfrequency. Thus, a change if any in concentration between chargedparticles in a part irradiated with acoustic waves cause a change instrength of the electromagnetic waves. By the way, since an object isneutral as a whole, if there exist positive charged particles there alsoexist negative charged particles of the same number and sinceelectromagnetic waves generated by positive charged particles and thosegenerated by negative charged particles are different by t in phase andcanceled by each other, it is apt to be considered that noelectromagnetic wave is radiated from the object. Such a situation israre, however. Even if in the part irradiated with acoustic waves thereexist positive charged particles and negative charged particles in thesame concentration, a difference between the positive and negativecharged particles in their mass, size, shape, or number of charges or ininteraction force of their surrounding medium, namely in their propertyvalue, makes a difference in amplitude between their harmonicoscillations, thus making a difference in strength between theelectromagnetic waves they produce which are not fully canceled out byeach other but emitted externally.

Thus, if a change has occurred in strength of electromagnetic wavesradiated from the part of an object irradiated with sound waves, itmeans that any one of concentrations, masses, sizes, shapes, and numbersof charges of charged particles and interaction forces of theirsurrounding medium or in a plurality of these property values of thecharged particles have been changed. That conversely, a change in suchproperty value of the charged particles can be determined from a changein strength of the electromagnetic waves. And, on what change in propervalues the change is based can be narrowed down on the basis of otherinformation on the object irradiated with sound waves. For example,assuming that the state is that the masses, sizes, shapes, numbers ofcharges and interaction forces with surrounding media cannot be altered,a change in strength of the electromagnetic waves can be tied to achange in concentration of charged particles in the part of an objectirradiated with acoustic waves.

Especially, in the case of a neuron when it is activated, a channel forNa ions on a cell wall is opened through which Na ions outside of a cellare diffused into the cell under their concentration gradient to form adistribution of Na ion charges, focusing sound waves on such a part tomeasure a strength of electromagnetic waves allows the strength of theelectromagnetic waves to largely vary with a neuron's action and permitsdetecting the neuron's action directly. Likewise, when a muscle tissueof a living body is made active where a charge distribution for Ca ionsis created, focusing acoustic waves on such a part to measure anintensity of electromagnetic waves allows the active site of muscletissue to be detected directly.

The present invention has been made based on principles as mentionedabove and will be described in detail hereinafter.

Accordingly, there is provided in accordance with the present inventiona method of measuring a property of an object with acoustically inducedelectromagnetic waves, characterized in that it comprises the steps of:irradiating a measurable object with acoustic waves; and measuringelectromagnetic waves generated from the measurable object to determineany one of properties of the object, including its electrical, magneticand electromagnetic mechanical properties, from any one or a combinationof strength, phase and frequency characteristics of the electromagneticwaves.

In the method mentioned above, the electric property determined of themeasurable object preferably includes a change or changes in one or moreof property values for electric field, dielectric constant, spatialgradient of electric field and spatial gradient of dielectric constantand for concentration, mass, size, shape and number of charges ofcharged particles which the measurable object possesses and forinteraction with a medium surrounding the charged particles. Themagnetic property determined of the measurable object preferablyincludes a property value for magnetization due to electron spin ornuclear spin in the measurable object or for acousto-magnetic resonanceattributable to electron spin or nuclear spin in the measurable object.The electromagnetic mechanical property preferably includes apiezoelectric property or magnetostriction property of the measurableobject.

According to the object's property measuring method of the presentinvention, if a change has occurred in a property value of chargedparticles contained in a part of the object irradiated with acousticwaves, namely in concentration, mass, seize, shape and number of chargesof charged particles or interaction force with their surrounding mediumor in a plurality of such property values, it is possible to determineany of electric property, magnetic property or electromagneticmechanical property from a change in intensity, phase or frequencycharacteristic of electromagnetic waves which then occur and can bedetected. For example, if there could be no possibility of change otherthan in the concentration of charged particles, a change in intensity ofelectromagnetic waves can be tied to a change in the concentration ofcharged particles. Also, if there could be no possibility of changeother than in the interaction force with the medium surrounding thecharged particles, a change in intensity of electromagnetic waves can betied to a change in polarizability of electrons or cations in thecharged particles. Further, as a magnetic property of the measurableobject, magnetization due to electron spin or nuclear spin, oracousto-magnetic resonance due to electron spin or nuclear spin can bemeasured, and as an electromagnetic mechanical property, piezoelectricor magnetostriction property of the measurable object can be measured.

The acoustic waves with which the measurable object is irradiated may bein the form of acoustic wave pulses and the electromagnetic waves can bemeasured of time dependence of their intensity detected subsequent toirradiation with the acoustic wave pulses to determine a relaxationcharacteristic of a property value for charged particles which themeasurable object possesses.

The acoustic waves can be in the form of those of a fixed frequency in anarrow band or acoustic wave pulses of a fixed frequency in a narrowband. The electromagnetic waves can then be measured at a highsensitivity, preferably by heterodyne or phase detection of theelectromagnetic waves radiated from the measurable object with afrequency of the acoustic waves as a reference signal. Then, externalnoises having other frequency components can be excluded to allowdetecting even a change very small in intensity of electromagneticwaves.

The acoustic waves of a fixed frequency in a narrow band can be in theform of pulses. Then, the electromagnetic waves are measured byheterodyne or phase detection of the electromagnetic waves radiated fromthe measurable object with a frequency of the acoustic waves as areference signal and heterodyne or phase detection of a signal resultingfrom the said detection with a pulse frequency of the said pulses. Inthis case, too, external noises having other frequency components canfurther be excluded to allow detecting even a change extremely small inintensity of electromagnetic waves.

Preferably, from phase information of the phase detection it isdetermined in which of positive charged particles or negative chargedparticles that the object possesses the electromagnetic waves as asignal are originated. Using the phase detection allows it to bedetermined from phase information in which of positive charged particlesor negative charged particles that the object possesses theelectromagnetic waves as a signal are originated.

A signal of said electromagnetic waves can be measured that is isolatedwith respect to time from electromagnetic noises occurring at a sourceof emission of said acoustic wave pulses if a time period for a saidacoustic wave pulse to propagate over a distance between the emissionsource of said acoustic wave pulses and said measurable object is chosento be longer than a pulse duration of said acoustic wave pulse or if thesaid pulse duration is made shorter than the said time period for theacoustic wave pulse to propagate, thus allowing detection of a changevery small in intensity of electromagnetic waves.

The measurable object is irradiated with acoustic waves preferably byfocusing acoustic waves from a plurality of a source on a desired smallpart of the measurable object and electromagnetic waves induced at thesmall part are measured with an antenna or coil means disposed tosurround the measurable object. Then, acoustic waves can be focused on adesired part and on the desired part from a desired direction andelectromagnetic waves radiated from a desired position and from thedesired positions towards a desired direction can be measured whiletheir radiation bearing distribution can be determined. When an objectis irradiated with acoustic waves, anisotropy in elasticity modulus ofcharged particles contained in the object may allow electromagneticwaves to be radiated in a direction different from that perpendicular tothat of the acoustic oscillations. Then, measuring the radiation bearingdistribution allows the type of charged particles and a change in theproperty value to be determined.

Preferably, focusing acoustic waves is scanned over a two-dimensionalsurface or three-dimensional volume of the measurable object and anintensity of induced electromagnetic waves at each scanning position ismeasured using an antenna or coil means surrounding the measurableobject to determine a two-dimensional or three-dimensional distributionof changes in a property value of charged particles of the object bycomparing the scanned position and the intensity of the measuredelectromagnetic waves.

The acoustic waves are preferably applied in the form of broadbandultrashort pulses composed of a plurality of frequency components. Then,the frequency of the electromagnetic waves can be measured so that fromthe measured frequency of electromagnetic waves, information may bederived on depthwise position of charged particles generating theelectromagnetic waves inasmuch as acoustic waves higher in frequencydamp faster and those lower in frequency arrive deeper in a brain or amuscle tissue of a living body. For example, it is possible to enhancethe accuracy in depthwise position information of the acoustic wavefocused part.

If the measurable object is a nervous tissue representative of a brain,a charge distribution can be formed when neuron is activated and if itis a muscle tissue of a living body, a charge distribution can likewisebe formed when the muscle tissue is activated. Since the intensity ofelectromagnetic waves grow with the charge distribution, atwo-dimensional or three-dimensional map of the activated site of brainor muscle tissue can be prepared if acoustic focusing is scanned over atwo-dimensional surface or three-dimensional volume of the brain ormuscle tissue, the intensity of electromagnetic waves induced at eachscanning position is measured with the antenna or coil means disposed tosurround the brain or muscle tissue and each scanning position and eachmeasured intensity of electromagnetic waves are made corresponding toeach other.

The method mentioned above is not limited to an object if it is a livingbody but can be applied to an object of any one of materials selectedfrom the group which consists of colloidal solution, liquid crystal,solid electrolyte, ionic crystal, semiconductor, dielectric, metal,magnetic material and magnetic fluid or a composite material thereof ora structure or a functional device composed of such a material, in whicha change in property value of charged particles can be measured to aidin clarifying the related phenomena.

The present invention also provides an apparatus for measuring aproperty of an object with acoustically induced electromagnetic waves,characterized in that it comprises an anechoic chamber, a retainer tablefor holding a measurable object disposed in the anechoic chamber, anacoustic generator disposed adjacent or in contact with the object, anantenna or coil means for receiving electromagnetic waves generated froma part which is irradiated with acoustic waves or pulses produced by theacoustic generator, and a control, measure and process unit for drivingand controlling the acoustic generator and for measuring and processingelectromagnetic waves received by the antenna or coil means.

The acoustic generator preferably comprises a plurality of acousticgenerators whereby acoustic wave pulses generated from the acousticgenerators are controlled of their mutual phase by the control, measureand process unit so as to be focused on a desired position of saidmeasurable object and the focusing position of acoustic waves is scannedover a two-dimensional surface or three-dimensional volume of themeasurable object.

The acoustic generator may comprise a plurality of acoustic generatorsfixed on a concaved surface whose normal is focused on a point. Then,the control, measure and process unit preferably drives these acousticgenerators simultaneously to generate acoustic wave pulses and at thesame time causes the acoustic generators fixed on the concaved surfaceto scan mechanically around the measurable object whereby the focusingposition of acoustic waves is scanned over a two-dimensional surface orthree-dimensional volume of the measurable object.

The control, measure and process unit preferably includes a means bywhich electromagnetic waves received by the antenna or coil means areheterodyne- or phase-detected with a frequency of the acoustic waves ora pulse frequency of the acoustic wave pulses. Then, external noisespossessed by other frequency components can be excluded to allow achange very small in intensity of electromagnetic waves to be detected.

A means is preferably included by which an electromagnetic wave signalresulting from detection by the said detecting means is locked in with apulse frequency of the acoustic wave pulses. Then, external noisespossessed by other frequency components can be excluded more to allow achange very small in intensity of electromagnetic waves to be detected.

The control, measure and process unit preferably comprises a means forcausing broadband ultrashort pulses to be generated from the acousticgenerator and a means for measuring a frequency of electromagnetic wavesreceived by the antenna or coil means. Then, it is possible to enhanceaccuracy in depth-wise position information of the acoustic wave focusedpart.

The means for measuring a frequency of electromagnetic waves preferablycomprises a bandpass filter provided in the control, measure and processunit.

The means for measuring a frequency of electromagnetic waves may alsocomprise a bandpass filter and a lock-in amplifier provided in thecontrol, measure and process unit. Then, external noises possessed byother frequency components can further be excluded to allow a frequencyof electromagnetic waves to be detected even if their intensity is verysmall.

The means for measuring a frequency of electromagnetic waves may alsocomprise a spectrum analyzer provided in the control, measure andprocess unit. Then, Fourier transformation by the spectrum analyzer ofelectromagnetic waves allow the intensity for each of frequencycomponents of electromagnetic waves to be detected and the frequency ofelectromagnetic waves to be determined from the frequency componentexhibiting the maximum intensity.

Effects of the Invention

According to the method and apparatus of the present invention,irradiating a measurable object with acoustic waves followed bymeasuring electromagnetic waves generated from the measurable objectallows any one of electric, magnetic and electromagnetic mechanicalproperties of the measurable object to be determined from any one or acombination of intensity, phase and frequency characteristic of theelectromagnetic waves measured. As an electric property of themeasurable object, any one or a combination of electric field,dielectric constant, spatial gradient of electric field or dielectricconstant, concentration, mass, size, shape, number of charges of chargedparticles that the measurable object possesses or interaction force withtheir surrounding medium can be measured of a change or changes thereof.As a magnetic property of the measurable object, magnetization due toelectron spin or nuclear spin, or acousto-magnetic resonance due toelectron spin or nuclear spin thereof can be measured. As anelectromagnetic mechanical property of the measurable object,piezoelectric or magnetostriction property of the measurable object canbe measured. Accordingly, measuring a change or changes in theseproperty values in a living body, colloidal solution, liquid crystal,solid electrolyte, ionic crystal, semiconductor, dielectric, metal,magnetic material or magnetic fluid or a composite material thereof or astructure or a functional device composed of such a material is usefulin clarifying the related phenomena. Especially, using the presentinvention in the determination of an active site in a brain makes itpossible to identify an activated site at an extremely high positionresolution.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Drawings:

FIG. 1 is a diagram illustrating a state that a part of an object isirradiated with acoustic waves to induce electromagnetic waves;

FIG. 2 is a diagram illustrating the structure of an apparatus formeasuring a property of charged particles in an object by means ofacoustically induced electromagnetic waves in accordance with thepresent invention;

FIG. 3 is a diagram illustrating a way of focusing acoustic waves;

FIG. 4 is a diagram illustrating an alternative way of focusing acousticwaves;

FIG. 5 is a block diagram illustrating the structure of a control,measure and process unit used in a first method of measurement accordingto the present invention;

FIG. 6 is a diagram illustrating a method of measuring a change withtime characteristic of a property value of charged particles inaccordance with the present invention;

FIG. 7 is a block diagram illustrating the structure of a control,measure and process unit used in a second method of measurementaccording to the present invention;

FIG. 8 is a block diagram illustrating the structure of a control,measure and process unit used in a third method of measurement accordingto the present invention;

FIG. 9 is a block diagram illustrating the structure of a control,measure and process unit used in a fourth method of measurementaccording to the present invention;

FIG. 10 illustrates a block diagram of the structure of a control,measure and process unit used in a fifth method of measurement accordingto the present invention wherein (a) shows the apparatus structure and(b) shows occurrence timings of gate pulses and acoustic generatingpulses produced by a pulse generator, those of acoustic waves generatedby an acoustic generator and those of electromagnetic waves induced inan object;

FIG. 11 is a block diagram illustrating the structure of a control,measure and process unit used in determining a polarity of charges of asource of emission of electromagnetic waves in the case of usingbroadband acoustic wave pulses;

FIG. 12 is a block diagram illustrating the structure of anothercontrol, measure and process unit used in determining a polarity ofcharges of a source of emission of electromagnetic waves in the case ofusing broadband acoustic wave pulses;

FIG. 13 diagrammatically illustrates the structure of an apparatus formeasuring a property of an object with acoustically inducedelectromagnetic waves in Example 1, showing at (a) the apparatusstructure, at (b) a modification of ultrasonic probe and at (c) awaveform of ultrasonic waves, respectively;

FIG. 14 illustrates detected waveforms of acoustically inducedelectromagnetic waves from semiconductor GaAs crystal as the object,showing at (a) an ultrasonic waveform, at (b) a waveform obtained in theproperty measuring apparatus in Example 1 and at (c) a waveform obtainedin a property measuring apparatus in Example 2;

FIG. 15 illustrates detected waveforms of acoustically inducedelectromagnetic waves from a measurable object, showing at (a) waveformfor Si crystal, and at (b) and (c) waveforms for GaAs crystals differentin crystal arrangement;

FIG. 16 illustrates detected waveforms in chart of acoustically inducedelectromagnetic waves, indicating at (a) a signal for hard osseoustissue of pig in Example 4, at (b) a signal for timber in Example 5, at(c) a signal for polypropylene in Example 6 and at (d) a signal foraluminum in Example 7; and

FIG. 17 is a chart of waveforms detected of acoustically inducedelectromagnetic waves from a ferrite magnet in Example 9.

DESCRIPTION OF REFERENCE CHARACTERS

-   -   1: acoustic beam    -   2: acoustic focused part    -   3: positive charged particle    -   4: negative charged particle    -   5: oscillating directions of acoustic waves    -   6: electromagnetic waves induced by acoustic waves    -   21: apparatus for property measurement with acoustically induced        electromagnetic waves    -   22: anechoic chamber    -   23: measurable object    -   23 a: acoustic focused part    -   24: retainer table    -   25: acoustic wave generator    -   26: acoustic waves    -   27: electromagnetic waves    -   28: antenna (array-type antenna or array-type coil)    -   28 a: element antenna    -   29, 30, 50, 52, 60, 65, 75, 76: a control, measure and process        unit    -   31: RF oscillator    -   31 a: RF signal    -   31 b: pulse signal    -   32: gate switch    -   33: pulse generator    -   34: amplifier    -   35: small signal amplifier    -   36: mixer    -   37: phase shifter    -   38: amplifier    -   39: low-pass filter    -   40: digital oscilloscope    -   41: personal computer    -   42, 62, 68, 78: signal line    -   43: time relaxation wave form of acoustically induced        electromagnetic waves    -   51, 61, 77: lock-in amplifier    -   54: broadband acoustic wave pulse    -   55, 57: band-pass filter    -   66: gate pulse    -   67: spectrum analyzer    -   69: pulse for generating acoustic waves

BEST MODES FOR CARRYING OUT THE INVENTION

Explanation is given hereinafter of best modes for carrying out thepresent invention:

At the outset, mention is made of how electromagnetic waves are inducedfrom an object when irradiated with acoustic waves.

FIG. 1 is a diagram illustrating a state that a part of an object isirradiated with acoustic waves to induce electromagnetic waves. In FIG.1, an acoustic wave focusing beam 1 is shown as focused on a part 2 of ameasurable object wherein positive charged particles 3 and negativecharged particles 4 are shown by + and − signs, respectively, which areencircled with circles. Also, in the part 2 of the object, the positivecharged particles 3 and the negative charged particles 4 lose theirbalance in concentration, exhibiting a charge distribution in which thepositive charged particles 3 predominate. The arrow 5 indicatesoscillating directions of acoustic waves whereas the arrow 6 indicatesthe electromagnetic waves produced with oscillations of the positive andnegative charged particles 3 and 4 by acoustic waves and propagating indirections perpendicular to the arrow 5.

As shown in FIG. 1, where the positive and negative charged particles 3and 4 when irradiated with the acoustic beam 1 are oscillated at afrequency of the acoustic waves in oscillating directions 5 of theacoustic waves, the oscillations which are of their charges induce theelectromagnetic waves 6 which propagate in the directions perpendicularto the oscillating directions 5. By the way, when the positive andnegative charged particles are oscillated identically, theelectromagnetic waves then produced, respectively, by the positive andnegative charged particles are deviated by t in phase and canceled outby each other so that no electromagnetic waves may be produced as awhole. In the part 2 of the object, however, having a chargedistribution in which the positive charged particles 3 are predominantso that there is no such cancelation, net electromagnetic waves 6 areinduced.

Thus, observing acoustically induced electromagnetic waves to observe achange in intensity of the electromagnetic waves makes it possible toascertain that a change has been brought about in charge distribution,namely that a change has occurred in concentration of positive chargedparticles 3 or negative charged particles 4 or both. To with, from themeasurement of acoustically induced electromagnetic waves it is possibleto determine a change in a property value, here concentration, ofcharged particles in the object.

While in connection with FIG. 1 the measurement of acoustically inducedelectromagnetic waves is shown to determine a change in concentration ofcharge particles, the property value of charged particles whose changecan be determined may be the mass, size, shape or number of charges ofcharged particles or interaction force with their surrounding medium asmentioned below.

Assuming that X: the position coordinate of a charge particle, M: themass of the charged particle, S: the effective cross-sectional area onwhich the charged particle receives a force based on acousticoscillations from its surrounding medium, p: the pressure of acousticoscillations, ν: the frequency of the acoustic oscillations and t: time,the equation of motion of the charged particle can be expressed byequation (1) below.

$\begin{matrix}{{M\frac{^{2}X}{t^{2}}} = {S\; p\; \sin \; 2\pi \; v\; t}} & (1)\end{matrix}$

The solution of this equation can be expressed by expression (2) below.

$\begin{matrix}{{X(t)} = {\frac{p\; S}{\left( {2\pi \; v} \right)^{2}M}\sin \; 2\pi \; v\; t}} & (2)\end{matrix}$

The oscillation amplitude A of the charged particle can be expressed byequation (3) below.

$\begin{matrix}{A \equiv \frac{p\; S}{\left( {2\pi \; v} \right)^{2}M}} & (3)\end{matrix}$

From equation (3) above, it can be seen that the amplitude A of thecharged particle varies with the mass of the charged particle. Also,since changing the size or shape of the charged particle changes theeffective cross-sectional area S on which the charged particle receivesthe force due to the acoustic oscillations from its surrounding media,the amplitude A of the charged particle is changed also by a change inthe size or shape. Further, since a change in interaction force with themedium surrounding the charged particle becomes a change in mass Mapproximately, it can be seen that a change in interaction force alsocauses a change in amplitude A of the charged particle.

Assuming that e is the charge of the charged particle, the oscillationsof the charged particle can be expressed as the harmonic oscillations ofcharge e by P=eA sin 2πνt. The radiating power I(t) of electromagneticwaves radiating from the oscillation P in a unit time with theassumption that ∈₀: vacuum dielectric constant and c: velocity of lightcan be expressed by equation (4) below.

$\begin{matrix}{{I(t)} = {\frac{1}{6\pi \; ɛ_{0}c^{3}}\left( \frac{^{2}P}{t^{2}} \right)^{2}}} & (4)\end{matrix}$

which if time averaged can yield equation (5) below.

$\begin{matrix}{I = {{\frac{1}{12\; \pi \; ɛ_{0}c^{3}}\left\lbrack {\left( {2\pi \; v} \right)^{2}e\; A} \right\rbrack}^{2} = {\frac{4\pi^{3}e^{2}}{3ɛ_{0}c^{3}}v^{4}A^{2}}}} & (5)\end{matrix}$

From equation (5) above, it can be seen that changing in amplitude Achanges the radiating power of electromagnetic waves. Accordingly, frommeasurement of the acoustically induced electromagnetic waves it can beseen that the mass, size, shape or number of charges of charged particleor interaction force with its surrounding medium can also be determined.For instance, if it can be assumed from other information on the stateof the measurable object or the knowledge gained by any other means thatthe concentration, mass, size, shape and number of charges are in thestate that cannot be altered, a change in strength of electromagneticwaves measured can be tied to a change in interaction force with themedium surrounding the charged particle, for example to a change inpolarizability of electrons or cations.

In the method of measuring a property of an object with the acousticallyinduced electromagnetic waves, the electric property that can bemeasured of the measurable object may be an electric field, a dielectricconstant or a spatial gradient of electric field or dielectric constant.

Assuming that ρ: the density of charges which the measurable object 23possesses, ρ can be related to the electric field according to thePoisson's equation (Gauss' law) as follows:

ρ=∇D=∇∈E=∇∈·E+∈·∇E  (6)

where D, ∈ and E are the electric flux density, dielectric constant andelectric field, respectively.

Since acoustically induced electromagnetic waves are caused by change ofthe charge density with time (∂_(ρ)/∂t) information on the chargedensity, namely on the electric flux density gradient can be acquiredfrom the intensity of electromagnetic waves. Further, in case theelectric field can be assumed to be spatially constant, then ρ=∇ ∈·E,the spatial gradient of dielectric constant can be obtained. In case thedielectric constant can be assumed to be constant, information on theelectric field gradient can likewise be acquired. In other words,electromagnetic radiation is microscopically created by chargeoscillation by charges which a measurable object possesses.Macroscopically, it can be considered that electromagnetic waves areradiated by the electric flux density, dielectric constant or electricfield changing with time. Accordingly, in measuring a function of aliving body, e.g., its brain function for analysis as well in accordancewith the method of the present invention, the acoustically inducedelectromagnetic waves have their root cause in change of intra-corporealion distribution with time and, with a sound focused area taken intoaccount which is more macroscopic than the ion scale, can be regarded asa means for measuring a change in electric flux density or electricfield gradient due to a neural activity.

In the method of measuring a property of an object with the acousticallyinduced electromagnetic waves, a magnetization due to electron spin ornuclear spin as the magnetic property of the measurable object can bemeasured as stated below. As with the electric polarization, anelectromagnetic radiation is generated by a magnetization changing withtime. According to the Maxwell's equation, a radiant electric field isproportional to the second derivative with respect to time of amagnetization (see Non-patent Reference 8). It follows, therefore, thatthe magnitude and direction of a magnetization can be determined fromthe strength or phase of electromagnetic waves.

In the method of measuring a property of an object with the acousticallyinduced electromagnetic waves, an acousto-magnetic resonance due toelectron spin or nuclear spin as the magnetic property of the measurableobject can be measured as stated below. From the fact that acousticwaves can efficiently be absorbed at a certain particular resonancefrequency to change the direction of electron spin or nuclear spin, itis anticipated that the strength or phase of electromagnetic waveslargely varies at that frequency. As the information, the resonancefrequency can then be fixed upon. The rest can be to scan, as in ESR(electron spin resonance) or NMR (nuclear magnetic resonance),frequencies of sound waves to obtain a spectrum, thereby making itpossible to obtain information on electron spin or nuclear spin. Also,the relaxation time of electron spin or nuclear spin can be measured.

In the method of measuring a property of an object with the acousticallyinduced electromagnetic waves, a piezoelectric or magnetostrictionproperty as the electromagnetic mechanical property of the measurableobject can be measured as stated below. An ionic crystal withoutinversion symmetry brings about an electric polarization according toits strain in principle. Thus, it is possible to derive the magnitude ofa polarization from the intensity of acoustically inducedelectromagnetic waves. Scanning acoustic waves allows imaging apiezoelectric property of a measurable object. Further, it is possibleto measure the piezoelectric tensor contactlessly without mounting anelectrode on a measurable object from the direction of propagation ofacoustic waves and the radiation distribution of electromagnetic waves.Since numerous bio-molecular crystals of bones or muscles in a livingbody have piezoelectric properties, their properties can be measurednon-invasively. As for bones, there is a treatment which is said to heala fracture sooner by irradiation with ultrasonic waves. There have beengrowing interest in researches on bones' piezoelectric properties. Themethod and apparatus of the present invention can provide a goodapplication for piezoelectric properties of bio-specimens.

In the method of measuring a property of an object with the acousticallyinduced electromagnetic waves, a magnetostriction as theelectromagnetic-magnetic property of the measurable object can bemeasured as stated below. The magnetostriction refers to a phenomenonthat an electron orbit is altered by crystal strain to add a change tothe electron spin magnetization through an orbit-spin interaction. Also,the crystal strain may bring about a change in crystal field splittingto alter the electron state, thereby altering the size of an electronspin magnetization. These changes with time are considered to generateelectromagnetic waves. Therefore, it is possible to determine arelationship between the magnitude of magnetization, the orbit-spininteraction or the crystal strain and the sensitiveness of the electronorbit change or between the crystal field splitting and the strainsensitiveness or between the crystal field splitting and the electronspin state from the intensity of acoustically induced electromagneticwaves. It is possible to measure the magnetostriction tensorcontactlessly and without mounting an electrode on the measurable objectfrom the direction of propagation of acoustic waves and the intensity ofradiation. The magnetostriction property can be imaged as can thepiezoelectric property be.

According to the method of measuring a property of an object withacoustically induced electromagnetic waves, irradiating a measurableobject with acoustic waves and measuring electromagnetic waves generatedfrom the measurable object allow any one of properties of the object,including its electrical, magnetic and electromagnetic mechanicalproperties, to be determined from any one or a combination of strength,phase and frequency characteristics of the electromagnetic waves. Thus,the electric property can be determined of said measurable object,including a change or changes in one or more of property values forelectric field, dielectric constant, spatial gradient of electric fieldand spatial gradient of dielectric constant and for concentration, mass,size, shape and number of charges of charged particles which themeasurable object possesses and for interaction with a mediumsurrounding the charged particles. The magnetic property can bedetermined of said measurable object, including a property value formagnetization due to electron spin or nuclear spin in the measurableobject or for acousto-magnetic resonance attributable to electron spinor nuclear spin in the measurable object. The electromagnetic mechanicalproperty can be determined including a piezoelectric property ormagnetostriction property of the measurable object.

An apparatus for measuring a property of an object with acousticallyinduced electromagnetic waves according to the present invention will bementioned next.

FIG. 2 is a diagram illustrating the structure of an apparatus 21 formeasuring a property of charged particles in an object by means ofacoustically induced electromagnetic waves in accordance with thepresent invention. Using the Figure, an explanation is given of thestructure and operation of the property measuring apparatus with theacoustically induced electromagnetic waves on the basis of chargedparticles which the object possesses.

The measuring apparatus 21 comprises an anechoic chamber 22, a retainertable 24 for holding thereon a measurable object 23 disposed in theanechoic chamber 22, an acoustic generator 25 disposed adjacent to or incontact with the object 23, an antenna 28 for receiving electromagneticwaves 27 generated from a region 23 a on which acoustic waves 26 arefocused that the acoustic generator 25 generates, and a control, measureand process unit 29 for controllably driving the acoustic generator 25and measuring and processing electromagnetic wave signals 27 received byone or more of element antennas 28 a of the antenna 28.

Here, the electromagnetic waves radiated from the measurable object 23can be measured of their near field or non-near field, namely far fieldmeasurement. As will be described later, a magnetic field such as anear-field of the electromagnetic waves emitted from the measurableobject 23 may be measured by SQUID. The antenna 28 may be an antenna ofany type that is capable of detecting electromagnetic waves. Forexample, an antenna of every kind such as a loop antenna or arrayantenna or that made up of a looped or arrayed coil can be used.

To operate the measuring apparatus 21 of the present invention, themeasurable object 23 is placed on the retainer table 24, acoustic wavesare generated from the acoustic generator 25, and electromagnetic waves27 radiated from the area 23 a on which acoustic waves are focused arereceived by any one or more of the element antennas 28 a of the arrayantenna or coil 28 for measurement at the control, measure and processunit 29. Also, scanning is effected over the area 23 a where acousticwaves are focused and electromagnetic waves 27 are measured for each ofthe scanning positions to determine an intensity distribution ofelectromagnetic waves over a two-dimensional surface or athree-dimensional volume of the object.

While the element antennas 28 a making up the array antenna 28 in FIG. 2are shown disposed on a circumference in a cross section of the arrayantenna 8. The element antennas 28 a are disposed at a uniform densitythereof over 4π radians around the object 23 so that they can receiveelectromagnetic waves induced from any desired part of the object orelectromagnetic waves induced, if acoustic waves are focused, from anydesired direction.

A way of and an apparatus for focusing acoustic waves on a desiredposition on a measurable object will be explained next.

FIG. 3 shows a way of focusing acoustic waves. This way is called aphased array method. Acoustic wave pulses 26 generated individually bypiezoelectric elements 25 arrayed in a row are focused by lagging andadvancing acoustic wave pulses 26 in phase more than those frompiezoelectric elements 25 lying towards the outside and inside of therow as shown. While the piezoelectric elements 25 are shown arrayed in asingle row, they may be arrayed in a plurality of lines step by step sothat acoustic wave pulses 26 generated by such piezoelectric elements 25may, when shifted appropriately in phase, be focused over athree-dimensional volume of the measurable object.

FIG. 4 is a diagram illustrating an alternative way of focusing acousticwaves. This way is called an acoustic lens method. Piezoelectricelements 25 are disposed on a concaved surface with a curvature suchthat each point thereon has a normal focused on a focal point togenerate acoustic wave pulses 26 simultaneously so that the individualacoustic wave pulses 26 propagate towards the focal point defined by theconcaved surface and are thereby focused. By mechanically scanning theacoustic lens around a measurable object, it is possible to focus at adesired site over a three-dimensional volume of the measurable object.The two ways described above can also be combined.

Mention is made specifically of the measuring method and apparatusaccording to the present invention.

An explanation is first given of a first measuring method and apparatusaccording to the present invention.

FIG. 5 is a block diagram illustrating the structure of a control,measure and process unit used in the first measuring method of thepresent invention. Using the Figure, the structure and operation of thecontrol, measure and process unit is described. The Figure shows thestructure where acoustic waves for irradiation are narrow band pulses ata fixed frequency. In FIG. 5, the control, measure and process unit 30is shown comprising an RF oscillator 31, a gate switch 32 for shaping anRF signal 31 a output from the RF oscillator 31 into a pulsed signal 31b of fixed shape, a pulse generator 33 for turning the gate switch 32 onand off and an amplifier 34 for amplifying the pulsed signal 31 b outputfrom the gate switch 32 and feeding the pulsed signal 31 b output fromthe amplifier 34 into the acoustic generator 25 for generating acousticwave pulses 26.

The control, measure and process unit 30 also comprises a small signalamplifier 35 connected to the array antenna 28 for amplifyingelectromagnetic waves received by the array antenna 28, a mixer 36 forphase-detecting the electromagnetic waves from the small signalamplifier 35 with an oscillation frequency ν of the RF oscillator 31, aphase shifter 37 for controlling the phase of an oscillation frequency νsignal of the RF oscillator 31 to furnish therewith and control themixer 36, an amplifier 38 for amplifying an electromagnetic wave signalpassed through the mixer 36, a low-pass filter 39 for passing frequencycomponents lower than at a fixed frequency selectively of theelectromagnetic wave signal amplified by the amplifier 38, and a digitaloscilloscope 40 for measuring the intensity of the electromagnetic wavesignal passed through the low-pass filter 39 in synchronism with pulsegeneration timings produced by the pulse generator 33. Also, indicatedby 33 a is a signal line for synchronizing the pulse generator 33 andthe digital oscilloscope 40.

The control, measure and process unit 30 also includes a personalcomputer 41. The RF oscillator 31, the pulse generator 33 and thedigital oscilloscope 40 are connected to the personal computer 41. Thepersonal computer 41 is used to control the RF signal 31 a and thepulsed signal 31 b, to acquire an electromagnetic wave signal measuredby the digital oscilloscope 40 and to control measurement by the digitaloscilloscope 40.

While in the description above the phase detection is shown as effectedwith the frequency of acoustic waves, it may be effected with thefrequency of acoustic wave pulses in which case the phase shifter 37 maybe connected to the pulse generator 33 to use the oscillation frequencyof the pulse generator 33 as a reference signal.

While in the Figure the structure of a controller is shown in which onlyone acoustic generator is driven, where a desired site of the object isto have acoustic wave pulses focused thereon and to be scanned inposition as described above, a plurality of acoustic generators as shownshould be provided together with a plurality of controllers as shownwhereby they are controllably driven. Using the phase detection whichcan exclude external noises contained in the other frequency componentspermits detecting even an extremely small change in intensity ofelectromagnetic waves. Also, with the phase detection which allows thephase of the reference signal to be varied with the phase shifter 37 andmeasured, it is possible to find which of positive or negative chargedparticles in oscillation the electromagnetic waves for measurement arebased on according to the positive or negative sign of a measured valuetaken when the electromagnetic waves and the reference signal arematched in phase.

Also, by selecting the distance d between the acoustic generator 25 andthe site of the object 23 to be irradiated with acoustic wave pulses toadjust the time period it takes an acoustic wave pulse to propagate overthe distance d to be longer than the time duration of an acoustic wavepulse or adjusting the duration of the acoustic wave pulse to be shorterthan that propagation time period, it is possible to ensure that theacoustically induced electromagnetic wave signal radiated from theobject can be measured upon separation in time from electromagneticnoises produced when the acoustic generator 25 generates acoustic wavepulses. In this case, as shown in FIG. 6, it is possible to measure atime dependent change in property value of charged particles containedin the object by measuring variations with time of the intensity ofelectromagnetic waves 43 detected subsequent to irradiation with anacoustic wave pulse 26. For example, a relaxation time by acousticexcitation of property value of the charged particles can be measured.

Mention is next made of a second measuring method and apparatusaccording to the present invention.

FIG. 7 is a block diagram illustrating the structure of a control,measure and process unit used in the second measuring method accordingto the present invention. The control, measure and process unit 50differs from that in the structure shown in FIG. 1 that a lock-inamplifier 51 is disposed between the low-pass filter 39 and the digitaloscilloscope 40. The lock-in amplifier 51 is used to detect, bylocking-in, an electromagnetic wave signal passed through the low-passfilter 39 with the oscillation frequency μ of the pulse generator 33used as a reference signal. Indicated by 42 is a signal line forsupplying the lock-in amplifier 51 with the oscillation frequency μ ofthe pulse generator 33.

According to this method in which both the frequency ν of acoustic wavesand the pulse period μ of acoustic wave pulses are used for phasedetection, it is possible to further exclude external noises having theother frequency components and to detect even an extremely small changein intensity of electromagnetic waves.

Here, the lock-in amplifier comprises a gate switch and a narrowbandamplifier for phase detection used for measurement based on the samemeasuring principles as those of phase detection. A lock-in amplifierhas been marketed having a set of gate switch and narrowband amplifierfor applications where the reference frequency for phase detection islow. Since the phase detection where the reference frequency is low iscustomarily called lock-in detection, the terms “lock-in amplifier” and“lock-in detection” are used here if the reference frequency for phasedetection low.

Mention is next made of a third measuring method and apparatus accordingto the present invention.

In a brain or muscle tissue of a living body, acoustic waves whosefrequency is higher damp quickly and those of lower frequency reachdeep. Consequently, measuring the frequency of electromagnetic wavesacoustically induced makes it possible to find if their emission sourceis deep or shallow. This phenomenon is utilized in the third method ofthe present invention. This method can be found from the frequencydetermined of electromagnetic waves if their emission source is deep orshallow to enhance its position resolution depthwise in an acoustic wavefocused part.

FIG. 8 is a block diagram illustrating the structure of a control,measure and process unit used in a third measuring method of the presentinvention. The control, measure and process unit 52 is devoid of the RFoscillator 31 in the structure of FIG. 1 and is configured so that asingle pulse 53 generated from the pulse generator 33 is applied to theacoustic generator 25. The acoustic generator 25 may comprise, e.g., apiezoelectric element. When the single pulse 53 is applied to thepiezoelectric element, the piezoelectric element will oscillate freelyuntil its oscillation energy is dissipated to become zero. Acoustic wavepulse 54 by the free oscillations of the piezoelectric element is awideband acoustic wave pulse in which frequencies are distributed over awider range than with the narrowband acoustic wave pulse 31 b in FIG. 1.

The control, measure and process unit 52 as shown has its measuringsection comprising a first bandpass filter 55 for passing particularfrequency components in an electromagnetic wave signal amplified by thesmall signal amplifier 35, the narrowband amplifier 38 for amplifyingthe frequency components transmitted through the first bandpass filter55, a second bandpass filter 57 for passing particular frequencycomponents in the frequency components amplified by the narrowbandamplifier 38 and the digital oscilloscope 40 for integrating thefrequency components passed through the second bandpass filter 57 tomeasure the intensity of electromagnetic waves.

In measurement using the control, measure and process unit 52, frequencycomponents of an electromagnetic wave signal are roughly chosen throughthe first bandpass filter 55, of which frequency components are finelyselected through the second bandpass filter 57. Intensities of theselected frequency components are measured of the electromagnetic wavesignal to identify the frequency of the electromagnetic waves from thefrequency exhibiting the maximum intensity. The depth-wise position canbe determined in the acoustic wave focused part from a frequency of themeasured electromagnetic waves.

According to this method, since acoustic waves higher in frequencyquickly attenuate and acoustic waves lower in frequency reach deeper ina brain or muscle tissue of a living body, it is possible to know adepthwise position of the acoustic waves in their focused part from afrequency of the measured electromagnetic waves.

Mention is next made of a fourth measuring method and apparatusaccording to the present invention.

FIG. 9 is a block diagram illustrating the structure of a control,measure and process unit 60 used in a fourth measuring method of thepresent invention. The control, measure and process unit 60 has itsmeasuring section which differs from that in the structure shown in FIG.8 only in that between the second bandpass filter 57 and the digitaloscilloscope 40 its control section includes a lock-in amplifier 61 thatuses pulse generation timings of the pulse generator 33 as a referencefrequency. Indicated at 62 is a signal line for supplying the lock-inamplifier 61 with pulse generation timings of the pulse generator 33 asa reference frequency.

In the third method, the intensity of electromagnetic waves is measuredby integrating electromagnetic wave signals by means of the digitaloscilloscope. This method integrates electromagnetic wave signalsexcluded of external noises by the lock-in amplifier 61 so that it canexclude external signals having other frequency components as well toenable a further smaller change in intensity of electromagnetic wavesthan with the third method to be detected.

Mention is next made of a fifth measuring method and apparatus accordingto the present invention.

FIG. 10 is a block diagram illustrating the structure of a control,measure and process unit used in a fifth measuring method of the presentinvention, showing the apparatus structure at (a). At (b) there areshown generation timings of gate pulses 66 and acoustic generatingpulses 69 produced by the pulse generator 33, those of acoustic waves 54generated by the acoustic generator 25 and those of electromagneticwaves 27 induced in an object.

The control, measure and process unit 65 as shown in FIG. 10( a) has itsmeasuring section comprising a small signal amplifier 35 for amplifyingreceived electromagnetic waves 27, the gate switch 32 by which anelectromagnetic wave signal amplified by the small signal amplifier 35is passed for a duration of the gate pulse 66 produced by the pulsegenerator 33 and a spectrum analyzer 67 for displaying with a frequencysignal the electromagnetic wave signal passed the gate switch 32. Thespectrum analyzer 67 has a function to detect and memorize the signalintensity for each of frequency components. The function of the spectrumanalyzer 67 can be processed by Fourier transformation at a processorequipped in the control, measure and process unit 65. A signal line 68is provided to supply the gate switch 32 with gate pulses 66 and asignal line 33 b is provided to synchronize the pulse generator inoperation with the spectrum analyzer 67.

As can be seen from the upper waveform chart in FIG. 10( b), a gatepulse 66 occurs in a time interval between two successive acoustic wavegenerating pulses 69. The lower waveform chart shows a timing ofgeneration of an acoustic wave pulse 54 produced at the acousticgenerator 25 by an acoustic wave generating pulse 69 and a timing ofgeneration of electromagnetic waves 27 induced upon arrival of theacoustic wave pulse 54 at the object 23. As shown, the gate pulse 66 andelectromagnetic waves 27 are made coincident in timing of generation.And, signals introduced into the spectrum analyzer 67 are only in timeintervals in which electromagnetic waves 27 are induced, therebyexcluding external noises in the other time intervals and making itpossible to detect a change extremely small in intensity ofelectromagnetic waves.

Mention is next made of a method of and an apparatus for determining apolarity of charges of a source of emission of electromagnetic waves inthe case of using broadband acoustic wave pulses.

FIG. 11 is a block diagram illustrating the structure of a control,measure and process unit 75 used in determining a polarity of charges ofa source of emission of electromagnetic waves in the case of usingbroadband acoustic wave pulses. The control, measure and process unit 75has its measuring section comprising the small signal amplifier 35 thatamplifies received electromagnetic waves, the mixer 36 by which theelectromagnetic waves amplified at the small signal amplifier 35 arephase-detected with an oscillation frequency ν of the RF oscillator 31,a phase shifter 37 for controlling the phase of an oscillation frequencyν of the RF oscillator 31 for supply to control operation of the mixer36, the amplifier 38 that amplifies an electromagnetic wave signalpassed through the mixer 36, the low pass filter 39 that passes onlycomponents of frequencies less than a certain frequency among theelectromagnetic signal amplified by the amplifier 38, and the digitaloscilloscope 40 for measuring the intensity of an electromagnetic wavesignal passed through the low pass filter 39.

Thus, in measurement, the reference signal is varied in phase by thephase shifter 37 until it is matched in phase with the electromagneticwave signal; then finding if the measured value is positive or negativemakes it possible to determine that the electromagnetic waves measuredare based by the oscillations of positive charged particles or ofnegative charged particles.

FIG. 12 is a block diagram illustrating the structure of anothercontrol, measure and process unit 76 used in determining a polarity ofcharges of a source of emission of electromagnetic waves in the case ofusing broadband acoustic wave pulses. The control, measure and processunit 76 has its measuring section which is the same in structure as thatin FIG. 11 except that a lock-in amplifier 77, in which reference signalis supplied from the oscillation frequency of the pulse generator 33, isincluded between the low pass filter 39 and the digital oscilloscope 40.78 is a signal line to supply the oscillation frequency of the pulsegenerator 33 to the lock-in amplifier 77. Since this method comparedwith that of FIG. 11 can exclude external noises having other frequencycomponents, this method is able to determine the charge polarity if theelectromagnetic waves are extremely small in intensity.

In the apparatus for measuring properties of an object with acousticallyinduced electromagnetic waves in accordance with the present invention,a magnetic field of electromagnetic waves from the measurable object 23can be measured using a SQUID (superconducting quantum interferencedevice). The SQUID is a device having one or two Josephson junctions ina ring formed of a superconductor. With one Josephson junction and withtwo Josephson junctions, it is referred to as RF-SQUID and DC-SQUID,respectively. The SQUID is a supersensitive magnetic sensor having aquantization phenomenon of superconductor and has a sensitivity morethan hundred times compared with the conventional sensor. The SQUID iscapable of detecting a feeble electric field as weak as onefifty-millionth of earth magnetism.

The control, measure and process unit 29, 30, 50, 52, 60, 65, 75, 76mentioned above can be made up having a computer, a display and amemory. If a given time of a time sequence signal of acousticallyinduced electromagnetic waves is Fourier-transformed in an algorithm ofthe fast Fourier transformation (FFT) by the computer, the time ofcomputation can then be shortened. Means for obtaining a Fourierspectrum to this end can be a DSP (digital signal processor) or FFT unitwhich is exclusive or dedicated without recourse to a computer. Also,while as regards the signal processing such as amplifying anddemodulating, individual circuit components and means for measuringfrequencies have been shown variously, they can be substituted by anintegrated circuit tailored for the receiver or DSP.

In the present method of measuring an object's property withacoustically induced electromagnetic waves, the magnetostrictionproperty as an electromagnetic-magnetic property of the measurableobject can be measured as stated below.

The magnetostriction is meant a phenomenon that crystal strain alters anelectron orbit so that a change in spin magnetization is added throughthe orbit-spin interaction. Or, the crystal strain may cause a change incrystal field splitting which changes the electron state, therebychanging the magnitude of electron spin magnetization. A change in thesewith time is thought to generate electromagnetic waves. Accordingly,from the intensity of acoustically induced electromagnetic waves, it ispossible to determine the magnitude of magnetization, the orbit-spininteraction or the relationship between the crystal strain and thesensitiveness of electron orbit change, between the crystal fieldsplitting and the sensitiveness of strain or between the crystal fieldsplitting and the electron spin state. From the acoustic propagationbearing and radiant intensity, it is possible to measure themagnetostriction tensor contactlessly or without an electrode mounted onthe measurable object. As is the piezoelectric property, themagnetostriction property can be imaged.

According to a method of measuring a property of an object byacoustically induced electromagnetic waves, upon irradiating themeasurable object with acoustic waves and measuring electromagneticwaves generated from the measurable object, it is possible to determineany of electric, magnetic and electromagnetic mechanical properties fromany one or a combination of the intensity, phase and frequencycharacteristic of the electromagnetic waves.

Thus, as electric property of the measurable object, any one of electricfield, dielectric constant, spatial gradient of electric field ordielectric constant, concentration, mass, size, shape and number ofcharges of charged particles that the measurable object possesses andinteraction with their surrounding medium or a change or changes in oneor more of these property values can be measured. As a magnetic propertyof the measurable object, magnetization due to electron spin or nuclearspin, or acousto-magnetic resonance due to electron spin or nuclear spinof the measurable object can be measured. As an electromagneticmechanical property of the measurable object, piezoelectric ormagnetostriction property of the measurable object can be measured.

Mention is next made supplementarily of the case that the method andapparatus of the present invention for measuring a property of an objectis applied to identifying an active site in a brain.

The operating frequencies of piezoelectric element currently used formedical care are 3.5 MHz, 5 MHz, 7.5 MHz, 10 MHz and 30 MHz. Assumingthat acoustic waves travel in a human body at a velocity of 1600m/second, acoustic waves of 7.5 MHz come to have a wavelength of 213 μmin a human body and, if used for a human body, can become focused on aregion of about 213 μm. It follows, therefore, that if the method of thepresent invention is applied to identifying an active site in a humanbrain using acoustic waves of frequency 7.5 MHz, it is then possible toidentify the active site in the brain at a resolution of 213 μm. The useof high-frequency acoustic waves of 100 MHz or more for the purpose ofdealing with other than human bodies makes a resolution of 10 μm or lesspossible.

Focusing acoustic waves has practically been applied in ways as shown inFIGS. 3 and 4 to the medical field, e.g., used in a modern therapywithout need for a surgical operation, such as extracorporeal shock wavelithotripsy (see Non-patent Reference 6) or treatment by high intensityfocused ultrasound (see Non-patent Reference 7) used for cancer therapy.As for a brain, it is preferred to irradiate acoustic waves via anacoustic matching layer on the cranial bones which is less transmissiveof acoustic waves. In so identifying an active area in a brain, theapparatus of the present invention for measuring an object's propertywith acoustically induced electromagnetic waves can be used formeasurement. In this case, the measured data of brain's acousticallyinduced electromagnetic waves are separately taken and the recorded datacan be analyzed by a computer.

Example 1

The present invention in further detail with reference to specificexamples will be mentioned.

FIG. 13 diagrammatically illustrates the structure of an apparatusmeasuring a property of an object with acoustically inducedelectromagnetic waves in Example 1, showing at (a) the apparatusstructure, at (b) a modification of ultrasonic probe and at (c) awaveform of ultrasonic waves, respectively.

As shown in FIG. 13( a), the measuring apparatus 21 comprises theanechoic chamber 22, the retainer table for holding thereon a measurableobject 23 disposed in the anechoic chamber 22, the acoustic generator 25disposed adjacent to or in contact with the object 23, a loop antenna 28for receiving electromagnetic waves generated from a region 23 a onwhich acoustic waves 26 are focused that the acoustic generator 25generates, and the control, measure and process unit 29 (not shown) forcontrollably driving the acoustic generator and measuring and processingelectromagnetic wave signals 27 received by the loop antennas 28. Theacoustic generator 25 comprises a pulser (Panametrics Inc., model5077PR) and an ultrasonic vibrator of polyvinylidene fluoride driven bythis pulser. The pulser produced a rectangular wave of 50 ns pulse widthat a repetition frequency of 100 to 500 Hz (see FIG. 13( c)). Theultrasonic vibrator was spaced from the measurable object 23 at adistance of 50 to 70 mm across a water medium used. The acoustic wavestraveling in water at a velocity of 1500 m/s, it turned out thatelectromagnetic waves ultrasonically generated from the measurableobject 23 occurred every 33 to 47 μs. The measurement by a broadbandunderwater microphone indicated that the ultrasonic waves were focusedon an area of 2 mm diameter at a position of the measurable object 23.

At the output side of the loop antenna 28, there are a pair of tuningcapacitors of variable capacitance whose output is input into a smallsignal amplifier via a line of coaxial cable or the like. As shown, thesmall signal amplifier is connected in turn to a first small signalamplifier having a voltage gain of 46 dB, a low pass filter, anattenuator, a second small signal amplifier having a voltage gain of 46dB, an attenuator, a diode limiter and a third small signal amplifierhaving a voltage gain of 55 dB. The output of the third small signalamplifier is input to the digital oscilloscope.

Example 2

An apparatus for measuring a property of charged particles was preparedwhich was identical to that in Example 1 except that the output of thethird small amplifier was heterodyne-detected. The mixer used was adouble balanced mixer.

Example 3

Using a semiconductor made of GaAs crystal as the measurable object 23,acoustically induced electromagnetic waves were detected with theapparatus of Example 1 or 2 for measuring a property of chargedparticles.

FIG. 14 illustrates detected waveforms of acoustically inducedelectromagnetic waves from semiconductor GaAs crystal as the object 23,showing at (a) an ultrasonic waveform, at (b) a waveform obtained in theproperty measuring apparatus in Example 1 and at (c) a waveform obtainedin a property measuring apparatus in Example 2. In the graph of FIG. 14,the abscissa axis represents time (in μs) and the ordinate axisrepresents the signal intensity (in arbitrary scale). The GaAs used wasa non-doped crystal of 350 μm thickness. Its [110] axis was aligned inorientation with the direction of wave number vector k of the incidentultrasonic waves. The GaAs is a material whose piezoelectric coefficientis expressed by equation (7) below.

|d ₁₄ ^(GaAs)|=2.7 pC/N  (7)

Accordingly, if the wave number vector of longitudinal acoustic mode ofthe GaAs is parallel to piezoelectric axis <110>, it is predicted thatelectromagnetic waves are generated.

FIG. 14( a) shows an ordinary ultrasonic echo signal. It is seen thatexcitation (0 μs) by a high-frequency pulse of about 9.25 MHz producesan ultrasonic echo with a delay of 88 μs.

As is apparent from FIG. 14( b), an electromagnetic wave signal is seento occur at 44 μs that is one half of the period, namely at an instantwhen GaAs is irradiated with ultrasonic waves. This measurement wasperformed with the charged particles' property measuring apparatus ofExample 1, where the small signal amplifier had an amplification degreeof 82 dB and the digital oscilloscope had an integration of 200 pulses(in 1 second). The electromagnetic waves obtained from the GaAs had anpeak to-peak signal intensity (Vp-p) of 68 μV.

As is apparent from FIG. 14( c), an electromagnetic wave signal is seento occur at 44 μs that is one half of the period, at an instant whenGaAs is irradiated with ultrasonic waves. This measurement was performedwith the charged particles' property measuring apparatus of Example 2using the heterodyne detection and gave rise to an electromagnetic wavesignal more lucid than that shown in FIG. 14( c).

FIG. 15 illustrates detected waveforms of acoustically inducedelectromagnetic waves from a measurable object 23, showing at (a)waveform for Si crystal, and at (b) and (c) waveforms for GaAs crystalsdifferent in crystal arrangement. In FIG. 15( a) to FIG. 15( c), theabscissa axis represents time (in μs) and the ordinate axis representsthe signal intensity (in arbitrary scale).

From FIG. 15( a) where the measurable object is of Si, it is seen thatno signal is detected. This is due to the fact that since Si is asingle-element semiconductor, it does not exhibit a piezoelectricproperty.

FIG. 15( b) and FIG. 15( c) are shown that the ultrasonic wave numbervector is oriented parallel to the (100) and (110) planes of GaAscrystal, respectively. When GaAs crystal is arranged to be excited byultrasonic wave, it is seen that a high frequency signal is detected(see FIG. 15( c)).

The inserted figure in FIG. 15 is a graph illustrating a waveform of anelectromagnetic wave signal generated from the GaAs crystal of FIG. 15(c) and transformed into a signal from a temporal range to a frequencyrange, specifically detected by the spectrum analyzer. In this insertedfigure in FIG. 15, the abscissa axis represents the frequency (MHz) andthe ordinate axis represents the signal intensity (arbitrary scale).

As is apparent from the inserted figure of FIG. 15, a high frequencysignal of 7.60 MHz was observed. This high frequency signal occurredfrom the resonance oscillation waveform of ultrasonic waves of GaAs andhad its Q (quality factor, also called voltage build-up rate) of about10. The frequency of 7.60 MHz, with the acoustic propagation velocity inGaAs of 4730 m/s taken into account is presumed to be due to amechanical resonance of one half wavelength corresponding to thethickness 350 μm of GaAs.

Example 4

As Example 4, acoustically induced electromagnetic waves from a rib of apig were detected. The bone is made up of 70% of hydroxyapatite and 20%of a fiber consisting of oriented collagen, of which it is known thatthe fiber consisting of oriented collagen has a piezoelectriccoefficient expressed by equation (8) below.

|d ^(bone)|≈0.1 pC/N  (8)

As the measurable object 23, a hard tissue of outer bone and a softtissue of inner bone were prepared from a 2 mm thick square plate ofbone cut out of the rib. The axis of the tissues was paralleled to thesurface of the plate. Such specimens were ultrasonically cleaned with anethanol solution for 1 hour. For all the specimens, the vector ofultrasonic waves is made perpendicular to the tissue axis. Ultrasonicpulses had a repetition frequency of 500 Hz to irradiate each of thebone specimens with ultrasonic waves via water for detection ofelectromagnetic waves. The gain of the small signal amplifier had set to97 dB. And, the digital oscilloscope was used for 10 minutes for signaldetection.

FIG. 16( a) shows a detected waveform of acoustically inducedelectromagnetic waves from the hard tissue of pig's bone in Example 4,wherein the abscissa axis represents time (μs) and the ordinate axisrepresents the signal intensity (arbitrary scale).

As is apparent from FIG. 16( a) it is seen that electromagnetic wavescan be detected from a hard tissue of a pig's bone. The soft tissue ofpig's bone was likewise measured and a waveform of electromagnetic wavesas in FIG. 16( a) could be detected. The piezoelectric coefficient of abone has so far been reported to markedly damp in water with ionscreening. As shown in Example 4, however, it was found thatelectromagnetic waves could be detected from a specimen of bone disposedin water. This indicates that the ion screening which is a phenomenonslower than in a MHz frequency band is negligible in the use of highfrequency pulses of about 10 MHz level as in the present invention.

Example 5

As Example 5, electromagnetic waves from timber were detected, whereinthe timber was irradiated with ultrasonic waves caused to propagatethrough a plastic tube (see FIG. 13( b)) as an ultrasonic probe. FIG.16( b) is a chart illustrating a detected waveform of acousticallyinduced electromagnetic waves from timber in Example 5. In FIG. 16( b),the abscissa axis represents time (μs) and the ordinate axis representsthe signal intensity (arbitrary scale). As is apparent from FIG. 16( b),it is seen that electromagnetic waves from timber can be detected. Inthis case it is presumed that timber which has cellulose as its maincomponent which exhibits piezoelectricity brings about electromagneticwaves.

Example 6

As Example 6, acoustically induced electromagnetic waves were detectedin a setup identical to that in Example 5 except that the measurableobject 23 was of polypropylene as a plastic material.

FIG. 16( c) shows a detected waveform of acoustically inducedelectromagnetic waves from polypropylene in Example 6. In FIG. 16( c),the abscissa axis represents time (μs) and the ordinate axis representsthe signal intensity (arbitrary scale). As is apparent from FIG. 16( c),it is seen that electromagnetic waves from polypropylene can be detectedthough its signal is extremely weak. In this case, it is presumed thatpolypropylene which is piezoelectric but feeble in signal outputgenerates electromagnetic waves from crystallized grains.

Example 7

As Example 7, acoustically induced electromagnetic waves were detectedin a setup identical to that in Example 5 except that the measurableobject was of aluminum.

FIG. 16( d) shows a detected waveform of acoustically inducedelectromagnetic waves from aluminum in Example 7. In FIG. 16( d), theabscissa axis represents time (μs) and the ordinate axis represents thesignal intensity (arbitrary scale). As is apparent from FIG. 16( d), itis seen that very strong electromagnetic waves from aluminum can bedetected. In the case of aluminum in which the longitudinal waves intheir acoustic mode change the bottom of a valence band via a potentialmodified interaction, it is presumed that electromagnetic waves aregenerated by this action causing the conduction electrons to be given adisplacement repetitively.

Example 8

As Example 8, acoustically induced electromagnetic waves were detectedin a setup identical to that in Example 5 except that the measurableobject was of copper. As a result, it was found that very strongelectromagnetic waves from copper as from aluminum could be detected.

Example 9

As Example 9, acoustically induced electromagnetic waves from ferritemagnets composed of SrO and Fe₂O₃ were detected.

FIG. 17 shows a detected waveform of acoustically inducedelectromagnetic waves from the ferrite magnet in Example 9. In FIG. 17,the abscissa axis represents time (μs) and the ordinate axis at the lefthand side represents the intensity of high frequency signal of 8 MHzdetected while the ordinate axis at the right hand side represents theintensity (arbitrary scale) of ultrasonic echo signal detected. It isseen that in a time range prior to arrival of acoustic waves at thespecimen, the electromagnetic waves are low in noise level butsubsequent to arrival of acoustic waves at the measurable object, theelectromagnetic waves grows in background level over a long time. Thissuggests that the acoustic waves once entering inside of ferrite repeatreflection back and forth inside of the measurable object. As a result,it is presumed that the electromagnetic waves continue to be radiatedover a time much longer than the acoustic waves are irradiated. Thus,from Example 9 it was found that acoustically induced electromagneticwaves could be detected from the measurable object if composed of amagnetic material, too.

The present invention is not limited to specific examples as mentionedabove and allows various modifications within the scope of the inventionset forth in the appended claims, which should, needless to say, fallwithin the scope of the invention.

INDUSTRIAL APPLICABILITY

As will be appreciated from the foregoing description, the use of amethod and apparatus of the present invention in which a measurableobject is irradiated with acoustic waves and electromagnetic wavesemitted from the measurable object are measured, allows any of electric,magnetic and electromagnetic mechanical properties of the measurableobject to be determined from one or a combination of intensity, phaseand frequency characteristic of the electromagnetic waves.

Thus, as the electric property of a measurable object, a change orchanges in one or more of property values for electric field, dielectricconstant, spatial gradient of electric field and spatial gradient ofdielectric constant, for concentration, mass, size, shape and number ofcharges of charged particles which the measurable object possesses andfor interaction with a medium surrounding the charged particles can bemeasured. As the magnetic property of a measurable object, a propertyvalue for magnetization due to electron spin or nuclear spin in themeasurable object or for acousto-magnetic resonance attributable toelectron spin or nuclear spin in the measurable object can be measured.As the electromagnetic mechanical property of a measurable object, apiezoelectric property or magnetostriction property of said measurableobject can be measured. Since a change or changes in one or more ofproperty values for concentration, mass, size, shape and number ofcharges of charged particles which the measurable object possesses andfor interaction with a medium surrounding the charged particles can thusbe measured, measurement of a change or changes in these property valuesin a living body, colloidal solution, liquid crystal, solid electrolyte,ionic crystal, semiconductor, dielectric, metal, magnetic material andmagnetic fluid or a composite material thereof or a structure or afunctional device composed of such a material allows aiding inclarification of a related phenomenon. Especially, using the presentinvention in the determination of an active site in a brain makes itpossible to identify an activated site at an extremely high positionresolution and hence is extremely useful.

1. A method of measuring a property of an object with acousticallyinduced electromagnetic waves, characterized in that it comprises thesteps of: irradiating a measurable object with acoustic waves; andmeasuring electromagnetic waves generated from said measurable object todetermine any one of properties of the object, including its electrical,magnetic and electromagnetic mechanical properties, from any one or acombination of strength, phase and frequency characteristics of saidelectromagnetic waves.
 2. The method of measuring a property of anobject with acoustically induced electromagnetic waves as set forth inclaim 1, characterized in that the electric property determined of saidmeasurable object includes a change or changes in one or more ofproperty values for electric field, dielectric constant, spatialgradient of electric field and spatial gradient of dielectric constantand for concentration, mass, size, shape and number of charges ofcharged particles which said measurable object possesses and forinteraction with a medium surrounding said charged particles.
 3. Themethod of measuring a property of an object with acoustically inducedelectromagnetic waves as set forth in claim 1, characterized in that themagnetic property determined of said measurable object includes aproperty value for magnetization due to electron spin or nuclear spin insaid measurable object or for acousto-magnetic resonance attributable toelectron spin or nuclear spin in said measurable object.
 4. The methodof measuring a property of an object with acoustically inducedelectromagnetic waves as set forth in claim 1, characterized in that theelectromagnetic mechanical property of the measurable object includes apiezoelectric property or magnetostriction property of said measurableobject.
 5. The method of measuring a property of an object withacoustically induced electromagnetic waves as set forth in claim 1,characterized in that the acoustic waves with which said measurableobject is irradiated are in the form of acoustic wave pulses and saidelectromagnetic waves are measured of time dependence of their intensitydetected subsequent to irradiation with said acoustic wave pulses todetermine a relaxation characteristic of a property value for chargedparticles which said measurable object possesses.
 6. The method ofmeasuring a property of an object with acoustically inducedelectromagnetic waves as set forth in claim 1, characterized in thatsaid acoustic waves are in the form of those of a fixed frequency in anarrow band or acoustic wave pulses of a fixed frequency in a narrowband and said electromagnetic waves are measured by heterodyne or phasedetection of the electromagnetic waves radiated from said measurableobject with a frequency of said acoustic waves as a reference signal andheterodyne or phase detection of a signal resulting from said detectionwith a pulse frequency of said pulses.
 7. The method of measuring aproperty of an object with acoustically induced electromagnetic waves asset forth in claim 1, characterized in that said acoustic waves are inthe form of acoustic wave pulses of a fixed frequency in a narrow bandand said electromagnetic waves are measured by heterodyne or phasedetection of the electromagnetic waves radiated from said measurableobject with a frequency of said acoustic waves as a reference signal andheterodyne or phase detection of a signal resulting from said detectionwith a pulse frequency of said pulses.
 8. The method of measuring aproperty of an object with acoustically induced electromagnetic waves asset forth in claim 6 or claim 7, characterized in that from phaseinformation of said phase detection, it is determined whether saidelectromagnetic wave signals originate from positively charged particlesor negatively charged particles possessed by said object to be measured.9. The method of measuring a property of an object with acousticallyinduced electromagnetic waves as set forth in any one of claims 5 to 7,characterized in that a signal of said electromagnetic waves is measuredthat is isolated with respect to time from electromagnetic noisesoccurring at a source of emission of said acoustic wave pulses bychoosing a time period for a said acoustic wave pulse to propagate overa distance between the emission source of said acoustic wave pulses andsaid measurable object so as to be longer than a pulse duration of saidacoustic wave pulse or by making said pulse duration shorter than saidtime period for the acoustic wave pulse to propagate.
 10. The method ofmeasuring a property of an object with acoustically inducedelectromagnetic waves as set forth in any one of claims 1 and 5 to 7,characterized in that said measurable object is irradiated with acousticwaves by focusing acoustic waves from a plurality of a source on adesired small part of said measurable object and electromagnetic wavesinduced at said small part are measured with an antenna or coil meansdisposed to surround said measurable object whereby acoustic waves arefocused on a desired part and on the desired part from a desireddirection and electromagnetic waves radiated from a desired position andfrom the desired positions towards a desired direction is measured whiletheir radiation bearing distribution is determined.
 11. The method ofmeasuring a property of an object with acoustically inducedelectromagnetic waves as set forth in claim 10, characterized in thatfocusing acoustic waves is scanned over a two-dimensional surface orthree-dimensional volume of said measurable object and an intensity ofinduced electromagnetic waves at each scanning position is measuredusing an antenna or coil means surrounding said measurable object todetermine a two-dimensional or three-dimensional distribution of changesin a property value of charged particles of said object.
 12. The methodof measuring a property of an object with acoustically inducedelectromagnetic waves as set forth in claim 1 or claim 5, characterizedin that said acoustic waves are applied in the form of broadbandultrashort pulses and that the frequency of said electromagnetic wavesis measured and from the measured frequency of electromagnetic waves,information is derived on depthwise position of charged particlesgenerating the electromagnetic waves.
 13. The method of measuring aproperty of an object with acoustically induced electromagnetic waves asset forth in any one of claims 1, 2 and 5 to 7, wherein said measurableobject is a nervous tissue representative of a brain or a muscle tissueof a living body, characterized in that a charge distribution formedwhen neuron or muscle tissue is activated is measured as changes inproperty value of charged particles to identify a site of said activatedneuron or said muscle tissue.
 14. The method of measuring a property ofan object with acoustically induced electromagnetic waves as set forthin any one of claims 1, 2 and 5 to 7, characterized in that saidmeasurable object is of any one of materials selected from the groupwhich consists of colloidal solution, liquid crystal, solid electrolyte,ionic crystal, semiconductor, dielectric, metal, magnetic material andmagnetic fluid or a composite material thereof or a structure or afunctional device composed of such a material, in which a change inproperty value of charged particles is measured. 15-20. (canceled)